The all solid tires for pneumatic tires rim of WonRay have a "Tire Wear Indicator". Like below piecures:

As the tires wear down, you can see it from tires side-wall easily. The indicator prevents unnecessary or early tire replacement and minimizes equipment downtime for cost savings. It also reduces waste and cuts a fleet’s carbon footprint when you are using a non-marking tires reducing the frequency of replacement part shipments.